There are known various gas detectors, in which the chemical composition is identified by mass analysis of ions occurring at the gas ionization (see, e.g. [1]). Measurement of the current of ions separated with respect to their charge-to-mass ratio provides determination of the qualitative and quantitative composition of the gas mixture. A common feature of these prior art methods with the one we are suggesting, is the ionization of impurities at an ionization chamber. One of disadvantages of these prior art approaches are large detector dimensions, because the ions with the different charge-to-mass ratio are selected and detected separately in a mass-spectrometer after a flight along a trajectory of definite length. Another disadvantage is the necessity to maintain a fairly high vacuum along this trajectory to prevent the ions from scattering in collisions with residual gas molecules.
Another way of identifying the gas composition is to measure the kinetic energy of electrons released at the gas ionization, if the energy of exciting particles, e.g. photons, is definite (see e.g. [2]). The difference between the known energy of photons and the measured kinetic energy of electrons provides information on the ionization potentials of atoms or molecules, from which the gas composition is identified. The energy distribution of photoelectrons and the known photo-ionization cross sections allow determination of the partial concentrations of the gas species. The common features of these prior art methods and the present invention are the impurities ionization in an ionization chamber and the current measurement. A demerit of this prior art way is a large size of the detector, as the electron energy analysis is also accomplished during a flight along a trajectory having a definite length. Besides, it is necessary to maintain a rather high vacuum along the trajectory to prevent the electrons from collisions with a residual gas.
There are known ionization detectors capable of detecting gas impurities presence from the variation in the ionization current when the gas is excited (e.g. [3-6]). Such detectors have a small size and can operate at various pressures, up to atmospheric one. U.S. Pat. No. 5,532,599 [7] is most closely related to the present invention in the entire combination of features and is chosen as the nearest analog. Their common features are that the impurity atoms or molecules are ionized in collisions with particles of definite energy (metastable helium (He) atoms) in an ionization chamber, the current across the electrode located in the chamber is measured as a function of the applied voltage, and the impurities are detected from the electrode current data. However, the nearest analog in question provides only an ascertainment of the fact that an impurity has appeared in the main gas but it fails to make a direct qualitative analysis (to identify the impurity atoms or molecules) or quantitative (to measure the impurity concentrations) one.